Iron is an essential micronutrient of phytoplankton. Iron plays an important role in many biological processes such as nitrogen assimilation, N2 fixation, photosynthetic and respiratory electron transport, porphyrin biosynthesis. Since photosynthesis by phytoplankton fixes nearly 40 percent of the global carbon, a study of the origin of iron in seawater and its relationship to phytoplankton is important. In this paper, we discuss the origin and concentration of iron in seawater, its relationship with phytop...